Digital video streams typically represent video using a sequence of frames or still images. Each frame can include a number of blocks, which in turn may contain information describing the value of color, brightness or other attributes for pixels. The amount of data in a typical video stream is large, and transmission and storage of video can use significant computing or communications resources. Due to the large amount of data involved in video data, high performance compression is needed for transmission and storage. In block-based codecs, this involves prediction techniques, including prediction using motion vectors.